- print_r: documentation ( source)
<?php
$validTo = DateTime::createFromFormat('Y-m-d H:i:s', '2015-10-31 15:32:00');
$validFrom = DateTime::createFromFormat('Y-m-d H:i:s', '2015-10-20 15:45:00');
$diff = $validTo->diff($validFrom, true);
print_r($diff);